All of the SRSs used in this evaluation were prepared by USGS personnel located in Lakewood, Colorado, and were analyzed for analyte concentrations and physical property values before mailing. A supply of these SRSs is maintained and is available to purchase by participating laboratories and USGS offices for use in their quality-control programs.
Trace constituents sample T-179 was prepared using water collected from Coal Creek southwest of Boulder, Colorado. The water was pumped through a 0.2- and 0.1-micrometer (mm) filter into a 1325-liter (L) polypropylene drum. The water was continuously circulated and passed through a 0.1-mm filter and ultraviolet sterilizer for 24 hours. The water was then acidified to a pH <2 with nitric acid (HNO3) and chlorinated to 5 parts per million (ppm) free chlorine with sodium hypochlorite. Some trace constituent concentrations were adjusted by adding reagent-grade chemicals. The sample was circulated through a 0.1-mm filter and an ultraviolet sterilizer for an additional 24 hours prior and during bottling. The 500-milliliter (mL) polypropylene bottles and caps were acid leached with 0.16N HNO3, deionized-water rinsed, and autoclave sterilized.
Major constituents sample M-172 was prepared using water collected from Chicago Creek near Idaho Springs, Colorado. The water was pumped through a 0.2- and 0.1-mm filter into a 1325-L polypropylene drum. The water was continuously circulated and passed through a 0.1-mm filter and ultraviolet sterilizer for 24 hours. The water was then chlorinated to 5-ppm free chlorine with sodium hypochlorite. Some major constituent concentrations were adjusted by adding reagent-grade chemicals. The sample was circulated an additional 24 hours, then allowed to sit for 48 hours. During bottling, the sample was pumped through an ultraviolet sterilizer and a 0.1-mm filter. The 500-mL polypropylene bottles and caps were acid leached with 0.16N HNO3, deionized-water rinsed, and autoclave sterilized.
Nutrient constituents sample N-83 was prepared in a 50-L polypropylene carboy using deionized water. This SRS was prepared a couple weeks prior to sample distribution. The water was circulated through a 0.1-mm filter and kept chilled with ice (12 degrees Celsius) during the entire preparation procedure. Ultraviolet sterilization was performed until the addition of reagent-grade chemicals. The 60-mL amber glass vials and teflon-faced rubber-lined caps were acid leached with 0.1N hydrochloric acid (HCl), deionized-water rinsed, and autoclave sterilized.
Nutrient constituents sample N-84 was prepared in a 190-L polypropylene drum using water collected from South Clear Creek south of Georgetown, Colorado. This SRS was prepared a couple weeks prior to sample distribution. The water was circulated through a 0.1-mm filter and kept chilled with ice (12 degrees Celsius) during the entire preparation procedure. Ultraviolet sterilization was performed until the addition of reagent-grade chemicals. The 250-mL polyethylene bottles were acid leached with 0.1N HCl, deionized-water rinsed, and autoclave sterilized.
Low ionic-strength constituents sample P-43 was prepared in a 600-L polypropylene drum with snow collected from Silverthorne, Colorado. The desired phosphate and fluoride concentrations were obtained by adding reagent-grade chemicals. Prior and during bottling, the sample was circulated through a 0.1-mm filter and an ultraviolet sterilizer. The 500-mL polypropylene bottles and caps were acid leached with 0.16N HNO3, deionized-water rinsed, and autoclave sterilized.
Mercury sample Hg-39 was prepared in a 45-L glass carboy using water collected from Chicago Creek near Idaho Springs, Colorado. It was preserved with 5 mL/L of 12 N HCl. The desired mercury concentration was obtained by adding a mercury standard solution. The 250-mL borsilicate glass bottles and teflon-lined caps were new, acid leached, and deionized-water rinsed.